As a semiconductor manufacturing technology and a communication technology have recently been developed, the mobile electronic device industry has expanded, and demands for environmental preservation and development of alternative energy due to resource depletion have increased, batteries have been actively studied. Since lithium primary batteries which are representative batteries have a higher voltage and higher energy density than conventional aqueous batteries, the lithium primary batteries may be easily made compact and light and thus are widely used. Such lithium primary batteries are mainly used as main power supply sources of mobile electronic devices or backup power supply sources.
Secondary batteries are rechargeable batteries formed of an electrode material having high reversibility. The secondary batteries are classified into cylindrical secondary batteries and polygonal secondary batteries according to outer appearances, and classified into nickel/metal hydride (Ni-MH) secondary batteries, lithium (Li) secondary batteries, and lithium-ion (Li-ion) secondary batteries according to anode and cathode materials. Devices to which secondary batteries are applied have been diversified from small devices such as mobile phones, notebooks, and mobile displays to medium and large devices for electric vehicles and hybrid vehicles. Accordingly, batteries are required to have high stability and cost effectiveness as well as lightweight design, high energy density, high charge/discharge speed, high charge/discharge efficiency, and excellent cycle characteristics.